Facile green synthesis route for new ecofriendly photo catalyst for degradation acid red 8 dye and nitrogen recovery

This study novelty is that new photo catalyst prepared from sustainability low cost precursors. Dark red color hydrogel composites have been easily prepared from gelatin biopolymer using a simple sol–gel method. Gelatin doped by cobalt chloride, and silver nanoparticles (SNPs) in the presence of traces amount of sodium dodecyl sulfate surfactant and calcium chloride. Water-insoluble Gelatin composites are thermally stable photocatalysts for the degradation of toxic anionic acid red 8 dye. Promising photodynamic activity confirmed by fluorescence emission at λmax 650 nm. Optical absorption in Vis. light enhanced photo catalytic activity. Silver nanoparticles enhanced crystallinity, and improved optical properties and porosity. Dopants by CoCl2 and silver nanoparticles increased band gap of gelatin composites from (1.82 to 1.95) indicating interfacial charge separation. Low band gaps improved photo catalytic activity. Optical band gaps (Eg) lower than 2.0 eV indicates high catalytic activity in the photo degradation acid red 8 dye using Vis. light, wavelength 650 nm. Percent removal efficiency (%Re) of the dye at 500 ppm initial concentration, pH 1, contact time 30 min., and 0.20 g L−1 dose photo catalyst reached 95%. pH not affects removal efficiency. So, gelatin composites removed AR8 dye by photodegradation mechanism rather than adsorption due to photodynamic activity. Kinetics of photodegradation followed pseudo first order kinetic with rate constant k1 5.13 × 10−2 min.−1 Good electrical conductivity and magnetic properties (effective magnetic moment (µeff 4.11 B.M) improved dye degradation into simple inorganic species. Nutrients NH4+, and NO3− degradation products recovered by using alumina silicate clay via a cation exchange mechanism.

www.nature.com/scientificreports/Salts mixture is continuously agitated in double distilled water till attaining homogeneous saturated solution that was filtered and left covered with porous filter paper.After 24 h., dark red viscous hydrogel is obtained.The hydrogel lyophilized, freeze dried at 4 °C under vacuum gave dark red powder that annealed at 120 °C for 2 h 38,39 .Visual appearance in Fig. 1.
PMMA resin increased mechanical strength of hydrogel to tolerate physical stress and improved shelf life.20 ppm AgNPs increased intensity of red color.Safe physical crosslinking assisted by heating-cooling cycle causing ionic interaction and intra molecular hydrogen bonding between gelatin chains leaving toxic nonbiodegradable residues 40 .Gelatin composite will be biodegradable have desirable habitat and be thermally stable with neither no unreacted monomer 41 .Physicochemical characteristics of AR8 dye 13 are represented as: Intense red color due to chromophores S = O, azo N = N, and auxochromes: sulphonic and OH functional groups.
A batch photodegradation experiment was carried out at low pH 3 (to enhance removal efficiency), different dose composite ultra-sonicated for 15 min.to increase surface area.Different initial concentration (C i ) of AR8 dye added with constant stirring at 50 rpm, adjusted at pH 3.0, and magnetic stirring continued for 30 min.to attain equilibrium adsorption of dye on the catalyst surface.At different time intervals, 5 mL suspensions were collected and centrifuged.For both samples in the dark and after light irradiation (100 W fluorescent Vis.light lamps incident on dye solution contain gelatin composite.Residual dye concentration in dark and light determined by UV-Vis.spectroscopy at λ max .508 nm using a calibration curve.Photo degradation followed in aqueous dye solution at pH 3, 0.20 g dose photo catalyst, illumination time 1.0 h.Residual dye concentration in terms of absorbance is converted into concentration using molar extension coefficient (slope of straight line equals, ε: 2*10 4 L mol −1 cm −1 19 obtained from application Beers Lambert law following least square method, correlation coefficient R 2 0.9984.
Degradation efficiency of AR8 dye equivalent to %Re 19 : where Co and Ct are initial and residual dye concentration respectively.Removal percentage (% Re) of AR8 by adsorption or photo catalysis at equilibrium calculated using relation 19 : where q e is AR8 dye concentration at equilibrium (mg/g), and C i , C e are initial and equilibrium dye concentration (mg L −1 ), V is solution volume, (L) and W mass (g) of photo catalyst.Degradation data are linear fitted to different kinetic models 42 : Zero-order kinetic model: where Q 0 , Q t are initial and released concentration respectively (almost, Q 0 = 0) and K 0 is zero order release constant, concentration.time−1 .

Pseudo first order (1°) kinetic
where k 1 is the rate constant of adsorption, min.−1 and t is contact time in min.Pseudo second-order (2°): Water absorption measurements (swelling) are carried out in triplicates (N = 3 for reproducibility) according to ASTM standard D-570-98.Composite sample is immersed in distilled water at 23 ± 2 °C for different time intervals.Sample is taken out from water and all surfaces debris are removed using clean dry cloth and accurately weighed.Water absorption is determined by weighing samples at regular time intervals 12 : where W1, W2 are sample weight before and after soaking respectively.

Ethical approval
There is no ethical issue in the manuscript.Authors approved consent on participation.

Results and discussion
Figure 2 shows FTIR spectra of gelatin composites: Bands assigned to characteristic stretching frequency (wavenumber, cm −1 ), with increasing wt.% CoCl 2 , band intensity at 3600 cm −1 -3000 cm −1 increased due to multiple OH groups.Vibration bands below 1000 cm −1 confirmed high force constant in Co-oxygen and Co-nitrogen bonds.Weak bands symmetric stretching NH, CH at 2812 cm −1 .The band at 3034-3062 cm −1 became much weaker, blue shifted to 2733 cm −1 on binding through N, O. Bands at 649, 1041, and 1622 cm −1 due to stretch C-N, N-N, C = N bonds respectively slightly shifted, intensified as doping increased electron cloud.Bands at 1227, 1276, 1428 cm −1 : C-N stretching, N-H deformation on binding CoCl 2 .Bands weakened and slightly shifted in position on doping.Intense band at 1378 cm −1 due to organic moiety of gelatin: AgNPs Bands at 520-537 cm (1) Re % = (Co − Ct) / Co × 100 Figure 3 (a-c) showed SEM surface micrographs: surface morphology of gelatin composites showed (2D arranged chains at a small spacing distance) on binding Co(II) ions.Microstructure changed from semi crystalline and more appearance capsule shape into crystalline structure in the presence of AgNPs.
Gelatin exhibited continuous polymeric chains.This structure changed on doping by cobalt chloride and decoration by AgNPs.Smooth structure due to high cross-linking between polymer chains.N atoms of gelatin binding oxygen atom via intra molecular H.B. and Van der Waals interaction gave uniform small micrometer particle size 17 .3D cross-linking increased surface area.PMMA chemically grafted hydrophilic functional groups of gelatins.Doping and grafting gelatin improved its polymer shell giving network hydrogel.NH, C = O, OH increases water entrapment into capillary porous.
Gelatin properties modified on doping.Sample 4 showed the most intense vibrational bands in FTIR spectra, so it was selected for further investigation.SEM images show changes in surface morphology of gelatin composites compared to native gelatin indicating grafting of dopants CoCl 2 and AgNPs to backbone chains of gelatin.
Amorphous composites improved catalytic activity.Figure 5 showed pXRD pattern foe AR8 dye after 5th repeated cycles reusibility.Retained pXRD pattern of hydrogel confirmed reusability for many repetitions due to: Chemical Stability (unchanged chemically after degradation organic pollutants).
Mechanical stability.Hydrogels must maintain their mechanical integrity throughout the swelling and deswelling by aqueous solutions during photo catalysis and photo stability against photo degradation.
Thermal stability of gelatin composite sample4 is confirmed in Fig. 6.In TGA.Curves, weight loss: below 200 °C due to dehydration; above 200 °C for gelatin units' degradation accompanied with phase change 15,19 .
Thermal behavior confirmed doping gelatin by cobalt chloride and AgNPs.TGA curves showed slight weight loss due to dehydration and loss both lattice and coordinated water molecules.DTA curves showed high Tm 240.71 °C confirmed thermal stability.In DSC, sample and reference sample have same or different masses and are kept at the same temperature.Energy given or removed from sample to maintain ΔT sample-reference , equal zero.The power energy change in the sample measured as a function of heat flow.Thermal transition changes specific heat and alters the power signal.Exothermic or endothermic peaks areas proportional to ΔH.Heat capacity C (heat Q absorbed by closed system of constant composition (dV = dN = 0) on heating 1 K 44 : Heat capacity at constant pressure C P differs than C V because Cv depends on internal energy and work done on volume expansion.For solids at low temperatures C P ≈ C V , when two pans heated, heat absorbed by the sample-temperature plot represent DSC curves.Heat flow: (heat, q supplied per unit time, t.Heating rate is temperature increase per unit time, t. www.nature.com/scientificreports/DSC represented in Fig. 7 explores thermal transitions: glass temperature Tg, crystallization, and melting.Above Tg: C P of sample increased and measured at the middle of the incline.T crystallization : above T g, mobility improved as kinetic energy increased atomic motion in ordered crystalline arrangements release heat. The area under the crystallization peak gave exothermic ΔH crystallization transition).Endothermic melting above T c at T melting that remains constant until complete melting, Area under peak equals latent heats of melting ΔH melting .Glassy and crystallization transition involves no peaks confirming the thermal stability of the gelatin composite, Table 2. www.nature.com/scientificreports/Above 100 °C, almost all sample showed glassy transition followed by crystallization and melting 32 .Small C P indicated the weak thermal conductivity of the samples confirming uses reduce thermal effect exothermic photo degradation.The hydrogel composite withstand waste heat from exothermic reactions occur during photo catalysis without significant thermal degradation.
The main factors: pH, temperature, dose, contact time, and initial dye concentration affecting experimental %Re of AR8 dye in dark and light identified from Plackett-Burman statistical analysis.Five independent variables were screened in six combinations, each variable organized, high ( +) and ( −) level.Averages %Re of duplicates determinations taken as responses 45 : %R −1 are high and low setting respectively.% R 0 .0 means no effect.Positive and negative main effects indicate variables near or apart from optimum respectively, Table 3.Control factors with effects magnitude qualified and statistically significant effects    www.nature.com/scientificreports/determined.Optimal conditions determined by combining levels of factors had the highest main effect.Student's t-test explored the statistical significance of regression coefficients of variables 45 .Parameters enhanced %Re are dose initial concentration and time.Temperature and pH were not affected.Strong electrostatic interaction on the surface of positively charged composite in solution below its pH of zero PZC (5.3) did not alter %Re indicated that gelatin composites act by photocatalysis, not adsorption.The surface charge of gelatin composite at different pH did not affect %Re.%Re was independent of temperature.Statistical parameters optimized in Table 4 25 .

Trials pH Contact time t°C Dose Agitation %R
In light, both Ci and light intensity control %R.The Fig. 8 UV-Vis.absorption spectra of native gelatin and gelatin composites due to electronic transitions from the ground state into the excited state.
Sample 4 showed three absorption peaks at 262, 314 and 715 nm.Weak absorption at 715 nm is due to intramolecular charge transfer.The spectral redshift of sample 4 (curve e) improved photo catalytic activity.Intensity of UV-Vis.absorbance bands depend on wt.% Co(II) ion for same chromophores 42 .
Figure 9 showed concentration dependence of band gap Eg that controlled UV-absorption coefficient depends on photon energy hυ : where ν frequency of incident radiation inversely proportional to wavelength (λ); A: constant depend on reduced masses of electron-hole pair and refractive index of the composite material and exponent r depends on nature of electronic transition; r = 2, ½ for indirect transition and for allowed direct transition respectively 42 .
Doping by CoCl 2 and AgNPs increased band gap of gelatin composites from (1.82 to 1.95) due to separation of charge (electron-hole) charge carries.All composite samples have suitable low Eg to be used as photo catalysts for dye degradation.
Linear portion of last curve extrapolated to x-axis to find the intercept (band gap).Low Eg (1.9-2.04 eV) confirmed good absorbance in Vis.Region indicated increase density of states available for electrons occupation and high photo catalytic activity 42 .
Figure 10 shows the nonlinear photo luminesce (PL) activity of gelatin composites on excitation at wavelength 340 nm.Optical activity: at 325-380 nm is attributed to charge transfer from gelatin ligand to Co(II) ion 44 .
Gelatin composites had large values of molar extension coefficients and long wavelength emission, Table 5 Sample 4 contained 20 ppm AgNPs (improved optical properties) showed the best optical activity.This composite sample showed intense absorption in Vis.region of electromagnetic radiation.
Catalytic efficiency reached 95% within 20 min.Cobalt dopant inhibited electron-hole recombination, decreasing Eg and improved photocatalytic properties, increased delocalization of electron density, and enlarged surface area 23,44 .
For 300 ppm AR8 dye completely degraded into colorless solution after 90 min.contact time.Kinetics firstorder model fitted photodegradation, R 2 = 0.9703.The ratio of residual concentration (Ct) to initial concentration (Co) decreases rapidly with irradiation time, Fig. 11.
Gelatin composite efficiently photo degrades AR8 dye without self-splitting because of inherent attractive forces retarding solubility.Hydrogel is an efficient photocatalyst in Vis.region light-driven photodegradation of AR8 with higher %Re than conventional La photocatalyst for other pollutants 19 .
Figure 12 shows a first-order plot for photodegradation data to a pseudo first-order kinetic model.Good straight line slope (correlation coefficient R 2 ) indicating that photodegradation of AR8 dye on gelatin composite followed pseudo-first order kinetically.Amount degradation unfitted to zero-order and second-order kinetic equations (R 2 less than 0.95).The reactant AR8 dye exists in too small concentration relative to the concentration of gelatin composite photocatalyst.The slope of the straight line equals rate constant k 1 5.13*10 −2 min −1 .The good straight line indicated degradation rates of AR8 dye increased with increasing irradiation time with dye decolonization more rapidly than La-perovskite photocatalyst for MB dye 42 .
Gelatin composite reused after immersion on 1.0 M NaOH solutions.Adsorbed hydroxyl removed dye molecules from active sites.

Degradation mechanism
Composite photocatalyst in an aerated aqueous solution contains AR8 irradiated under Vis.photon energy (hν), λ max .600 nm → electron (e − )-positive hole (h + ) pairs adsorbed on catalyst surface giving OH radical.Excited electron in the conduction band (CB) of gelatin composite affects adsorbed oxygen molecules from water at composite/solution interface giving superoxide radical O   www.nature.com/scientificreports/Optically active composites are with high carrier dynamics (e-hole) separation enhanced photo degradation.This mechanism could be schematically represented as following image (Fig. 13).
Holes generated in VB of catalyst oxidize dye and react with super-oxides radical, generating OH .radicals degraded dye via one-electron redox reaction forming CO 2 , sulphate, nitrate, and H 2 O. Nitrogen compounds NH 4 + , and NO 3 − recovered by using porous clay alumina silicate adsorbent to be used in agricultural fertilizers.Photocatalytic activity of AgNPs on gelatin composite exceeded that of removal methylene blue (MB) over nano sized La based photocatalyst under irradiation by Vis.Light (catalytic efficiency 69% in 100 min.illumination time) 47 .
AR8 extensively polluted wastewater from textile industries and its degradation has not been reported by photocatalysts such as metal oxides and semiconductors.Efficient semiconductor catalysts with low Eg absorb in Vis.light irradiation at ambient temperature and pressure 42 .Insoluble thermally stable gelatin composite is low cos.non-toxic and easily prepared by facile low cost methods.
Electrical properties confirmed photocatalytic properties.The rough surface of the gelatin composite (sample 4) has many cavities with variable particle sizes and shapes that improve catalytic activity, Table 6.
Dopants CoCl 2 and AgNPs improved photocatalytic activity by enhancing the hole-doping level and decreasing Eg.Large surface area composite enhanced photodegradation of dye.All constituents of gelatin composite are safe and have no toxicity on ecosystem 48 , Fig. 12.
Detected ions (Co (II) and Ag(I) leaching from gelatin composite during photo degradation below undeletable limitsAR8 dye ensure safety and environmental compatibility.No ion replenishment needed.Regeneration of photo catalysts required activity over prolonged periods for ensuring economic and environmental sustainability.Regeneration restoring active sites and structural integrity after fouling or consumption during photo catalysis via: washing photo catalyst with distilled water to remove adsorbed dye; Photo activation by light, simply  www.nature.com/scientificreports/exposing them to UV or Vis.light depending on photo catalyst's activation range) help breaking down adsorbed pollutants, essentially self-cleaning active sites.In some cases, a mild chemical treatment dissolve any strongly adsorbed dye molecules.This could involve mild acids, bases, or oxidizing agents that do not damage the photo catalyst itself.Annealing at 60 °C in vacuum oven 1.0 h regenerate photo catalyst by decomposing adsorbed dye organic compounds.Ultrasonic waves dislodge dye molecules from active sides, cleaned with 50 mL 1.0 M NaOH.High pH causes desorption of dye molecules.Regeneration by 4.0 M NaCl increases ionic strength by factor 0.4 causing desorption of dye molecules.Each regeneration process must be tailored to specific photo catalyst and its application, considering factors such as contaminants nature of the, hydrogel composition, and economics of regeneration process.Regeneration frequency and the number of effective regeneration cycles a photo catalyst can endure are critical factors that determine the lifecycle and cost-effectiveness of the photo catalyst.

Photodynamic activity of gelatin composites
Gelatin composite showed good optical activity: Absorption bands at 299-401 nm assigned to intra ligand metal charge transfer transition.Bands at 439-558 nm due to magnetic Oh geometry ((µ eff .4.11 B.M).
Optically active photosensitizer (S) molecules absorb and are excited by Vis.light photon (h υ ) energy.Excited S*molecule rapidly interact with inert triplet 3 O 2 molecular oxygen in water producing reactive free radicals reactive oxygen species (ROS): singlet oxygen, hydroxyl radicals (OH), and superoxide (O 2 − ) ions through charge transfer.ROS radicals contribute to oxidative damage of AR8 dye.Singlet oxygen 1 O 2 species rapidly attack organic dye molecules.Energetic 1 O 2 is very short-lived and rapidly relaxes to 3 O 2 after dye oxidation.
S* had: efficient ISC and high T-state quantum yield (Φ T ) and long τ allow interact with the oxygen of water.https://en.wikip edia.org/ wiki/ Photo dynam ic_ thera py-cite_note-:0-5 An electron in an S moleculehttps:// en.wikip edia.org/ wiki/ Elect ron is excited to a higher-energy orbital, elevating the chromophore from So into short-lived, electronically excited singlet state (Sn).Chromophore* loses energy by rapid decay through vibrational and rotational sub-levels in Sn via internal conversion (IC) to populate S1 before rapid relaxation to So. Radiative fluorescence (F) decay (S1 → So), lifetimes (τ F .10 −9 -10 −6 s.) spin allowed transitions S → S or T → T conserve spin multiplicity of the electron.S1 undergoes spin inversion and populate lower-energy first excited triplet state (T1) via (ISC) spin-inversion forbidden transition followed by second spin-forbidden to depopulate excited triplet state (T1) by decaying So (phosphorescence (P) (T1 → So).(τ P 0.001-1 s.) Longer than τ F
Transition metal Co(II) ion had high quantum yield (Φ T ) and nano sec.τ T showed no self-quenching of light photons before conversion 3 O 2 into 1 O 2 50 .High thermal stability of molecular structure.The dark red color confirmed that optically active chromophores interact with light photons 50 .
Dimensional stability explained improved performance of hydrophilic composites (water absorption and thickness swelling) by aqueous dye solution is essential event for photo catalysis in aqueous solutions, Fig. 15.Water easily penetrates polymer chain of hydrogel.Doping by AgNPs and CoCl 2 decreased swelling by restriction chains movement.

Electrical properties of gelatin composites
Total conductivity σ tot and dielectric parameters εˋ, εˋˋ calculated by using data of impedance (Z), capacitance (C), resistance (R), and phase angle (ϕ) at any frequency Fig. 16  where α: 0-1.Extent distribution τ increases with increasingα, τ o and decreases in heating.Constant τ o characterizes relaxation time (single oscillation of dipole in a potential well, E o free energy of activation for dipole relaxation, τ: average most probable spread relaxation time.
σ tot constant at low frequency range for all samples and obeys a power relation at high-frequency range 51 : where σ dc conductivity independent on frequency (extrapolation σ tot at ω = 0) σˋ(ω) is Ac conductivity.Frequency dependence fitted using a power low: where C, t, and A are capacitance, thickness, and cross-sectional area of the sample respectively and ε o 8.85 × 10 −12 F/m permittivity of free space.Figure 17 illustrates plot εˋ against frequency at different temperatures.Decease εˋ with increasing frequency reflects dielectric properties, ions motions, and polarity of composite.Ions rotate around their negative sites at short-distance transport (hop out of sites with low free energy barriers and pile up at sites with high free-energy barriers (ΔG activation impeding ions diffusion that vary from site to site gives different ionic motions).In electric field ion motions contribute to dielectric response cause AC conductivity.Variation dielectric properties with frequency indicating polarity.Due to dipole polarization, when AC frequency increases, ε decrease at high frequency, dielectric behavior represented in Fig. 17   log σ tot (ω) against frequency F, Hz at room temperature showed AC conductivity increases on increasing frequency due to impedance decrease, Fig. 18.
Good electrical conductivity and magnetic properties (effective magnetic moment 4.11 B.M) improved dye degradation into simple inorganic anion 51 .Variation AC conductivity with temperature, Fig. 19 indicated semiconducting properties and dielectric permittivity properties of metallic gelatin composite showed semiconducting behavior 52 .
AgNPs enhanced AC electrical conductivity 2.3 ×10 4 Ohm.cm −1 due to high electron density.This behavior explored that gelatin composites are semiconductors that have empty CB and full valence Band (VB) in electronic structure.
Figure2shows FTIR spectra of gelatin composites:Bands assigned to characteristic stretching frequency (wavenumber, cm −1 ), with increasing wt.% CoCl 2 , band intensity at 3600 cm −1 -3000 cm −1 increased due to multiple OH groups.Vibration bands below 1000 cm −1 confirmed high force constant in Co-oxygen and Co-nitrogen bonds.Weak bands symmetric stretching NH, CH at 2812 cm −1 .The band at 3034-3062 cm −1 became much weaker, blue shifted to 2733 cm −1 on binding through N, O. Bands at 649, 1041, and 1622 cm −1 due to stretch C-N, N-N, C = N bonds respectively slightly shifted, intensified as doping increased electron cloud.Bands at 1227, 1276, 1428 cm −1 : C-N stretching, N-H deformation on binding CoCl 2 .Bands weakened and slightly shifted in position on doping.Intense band at 1378 cm −1 due to organic moiety of gelatin: AgNPs Bands at 520-537 cm −1 confirmed Co-N, Co-O bonds, and C-N.Peaks (NH 2 : symmetric, anti-symmetric NH and CN stretching.Intense band at 1380-1385 cm −1 : C = C bond.Native gelatin retained in composites, peaks at 3460, 2920 to 2885, 1647, 1384, 1152, 1075, 1028, 557 cm −1 due to O-H, C-H, O-H, C-N, C-O(H), C-O-C stretching respectively.Co(II) ion binding gelatin via electron donors heteroatoms via N, O atoms.High delocalized electron density attained by dispersed AgNPs on gelatin polymeric matrix υ C=N , affected by interaction between Co(II) and π-electrons of C = O.Band at 1510-1608 cm −1 due to stretching vibration C = N bonds.Coordination bond formed between ketonic C = O group of gelatin and Co(II) ion.Bonding includes Cl − ion and coordinating water molecules.The most intense vibrations bands of sample confirmed strong bonding 43 .
Fig. proved hydrogel had 60% for 5th consecutive photo degradation.Biocompatible PMMA increased mechanical strength.Light stability: device tested under illumination without elevated temperatures.Heat stability: device tested without illumination at high temp (T).Shelf stability: without illumination at room T. Atmosphere humidity of stability tests not indicated.Light soaking tests (continuous 1-sun illumination) damp-heat stressors (85 °C, 85% relative humidity (RH)): Composites 90% initial wt.after 60 h in ambient atmosphere (20-30% RH) under 0.7-sun illumination.High wt.% PMMA 95% initial wt.photo stability: composite kept 100% wt. in dark, 96% on exposure inert atmosphere 10.488 h at 25 °C, illuminated at 1 sun in N 2 at 25 °C for 100 h, wt. drop to 90% due heterogeneous interfacial layers.Lifetimes: composite retain 91 wt.% after one year aging.Phase stability: SEM micrograph, Figure after Vis.light illumination showed no phase segregation.There is no lattice Instabilities induced by strain.

Figure 11 .
Figure 11.Variation of Ct/Co in photodegradation AR8 dye on the composite hydrogel.

Figure 12 .
Figure 12.Linear fitting of photodegradation data to pseudo first-order kinetic.

Figure 18 .
Figure 18.Dependence of AC conductivity on temperature and frequency.

Table 1 .
Chemical composition and physical characteristics of the hydrogel.

Table 2 .
Thermal transitions and DSC parameters.

Table 3 .
Plackett -Burman matrix and levels of independent variables affect %Re.

Table 5 .
Molar extinction coefficients (ε) corresponding to wavelength of absorption and emission.